cs89712 Cirrus Logic, Inc., cs89712 Datasheet - Page 61

• Manufacturer Part Number: cs89712
• Description: High-performance, Low-power System-on-chip With 10base-t Ethernet Controller
• Manufacturer: Cirrus Logic, Inc.

mand is issued, or if the entire frame has been read.
See Section 2.32, “Basic Receive Operation”.
2.33 Receive Frame Address Filtering
The Ethernet port is equipped with a Destination
Address (DA) filter used to determine which re-
ceive frames will be accepted. The DA filter can be
configured to accept the following frame types:
2.33.1 Individual Address Frames
For all Individual Address frames, the first bit of
the DA is a "0" (DA[0] = 0), indicating that the ad-
dress is a Physical Address. The address filter ac-
cepts Individual Address frames whose DA
matches the Individual Address or whose hash-fil-
tered DA matches one of the bits programmed into
the Logical Address Filter (the hash filter is de-
scribed later in this section).
2.33.2 Multicast Frames
For Multicast Frames, the first bit of the DA is a "1"
(DA[0] = 1), indicating that the frame is a Logical
Address. The address filter accepts Multicast
frames whose hash-filtered DA matches one of the
bits programmed into the Logical Address Filter
(the hash filter is described later is this section). As
shown in
cepted as Multicast frames under a very specific set
of conditions.
2.33.3 Broadcast Frames
Frames with DA equal to FFFF.FFFF.FFFFh are
broadcast frames. In addition, the CS89712 can be
configured for Promiscuous Mode, in which case it
will accept all receive frames, irrespective of DA.
2.33.4 Destination Address Filter
The DA filter is configured by five DA filter bits in
the RxCTL register: IAHashA, PromiscuousA,
MulticastA, IndividualA, and BroadcastA. Four of
these bits are associated with four status bits in the
RxEvent register: IAHash, Hashed, IndividualAdr,
and Broadcast. The RxEvent register reports the re-
DS502PP2
Table
28, Broadcast Frames can be ac-
sults of the DA filter for a given receive frame. See
Section 3.18.4 on page 119 for RxCTL details.
The IAHashA, MulticastA, IndividualA, and
BroadcastA bits are used independently. As a re-
sult, many DA filter combinations are possible. For
example, if MulticastA and IndividualA are set,
then all frames that are either Multicast or Individ-
ual Address frames are accepted. The Promiscu-
ousA bit, when set, overrides the other four DA
bits, and allows all valid frames to be accepted.
Table 29
available for DA filtering.
It may become necessary for the software to change
the Destination Address (DA) filter criteria without
resetting the Ethernet port. This can be done as fol-
lows:
1) Clear SerRxON (LineCTL register bit 6) to pre-
2) Modify the DA filter bits (B, A, 9, 7, and 6) in
3) Set SerRxON to re-enable the receiver.
Because the receiver has been disabled, the
CS89712 will ignore frames while the software is
changing the DA filter.
2.33.5 Hash Filter
The hash filter is used to help determine which
Multicast frames and which Individual Address
frames should be accepted by the CS89712.
2.33.5.1 Hash Filter Operation
See
passed through the CRC logic, generating a 32-bit
CRC value. The six most-significant bits of the
CRC are latched into the 6-bit hash register (HR).
The contents of the HR are passed through a 6-to-
64-bit decoder, asserting one of the decoder’s out-
puts. The asserted output is compared with a corre-
sponding bit in the 64-bit Logical Address Filter,
vent any additional receive frames while the fil-
ter is being changed.
the RxCTL register. Modify the Logical Ad-
dress Filter, if necessary.
Figure
summarizes the configuration options
21. The DA of the incoming frame is
CS89712
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